Integrable mixed-valence impurity in a one-dimensional correlated electron lattice Original Research Article

We consider spin-12 electrons on a chain with nearest neighbor hopping t constrained by the excluded multiple occupancy of the lattice sites, and spin-exchange J and charge interaction between neighboring sites. The model is integrable at the supersymmetric point, J = 2t, where charges and spin form a SU(3) superalgebra. The model differs from the traditional t-J model, where the supersymmetry arises as a graded FFB permutation, rather than a BBB algebra. Without destroying the integrability of the model we introduce an impurity of arbitrary spin S, which hybridizes with the conduction states of the host. The discrete Bethe ansatz equations diagonalizing the correlated host with impurity are derived and the solutions are classified according to the string hypothesis. The thermodynamic Bethe ansatz equations and the impurity free energy are obtained. The ground state properties of the host and the impurity are studied as a function of the band-filling and the Kondo exchange coupling. The impurity has a magnetic ground state for S > 12 and in general mixed valent properties.